*ATTEN
10dB
RL
0dBm
lOdB/
I
I
I
CENTER
300.0000MHz
*RBW
1.0MHz
VBW 1
.BMHz
SPAN
3.000MHz
SWP 50ms
SK183
Figure 9-14. Faulty LC Pole
30
kHz
Resolution
Bandwidth
Problems
Shape factor too high: Shape factor is the ratio of the 60 dB bandwidth to the 3 dB
bandwidth. Shape factor should be less than
15:l.
If one of the LC poles malfunctions, the
shape factor may be the only indication of the failure. Isolate the non-functioning pole with
the IF signature. Region E of Figure 9-8 illustrates the four LC-pole adjustments. Take
several signatures to examine the LC-pole adjustments. If one of the four sections of Region E
is consistently longer than the others, the corresponding LC pole is faulty.
IF gain compression: FET transistors Q301, Q303, Q700, and
Q701
can deteriorate with age.
Measuring less than 0 volts on the FET source indicates a bad FET.
Bandwidth too wide: Check for contamination on the printed-circuit board. Clean the board
as required.
3
kHz
and
10
kHz
Resolution
Bandwidth
Problems
Asymmetric Filter Response: Check the crystal symmetry control with the following steps:
1. Press
(KZZiJ
2. Set the HP 85623 spectrum analyzer controls as follows:
Resolution bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 kHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
100kHz
Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
3. On the HP 85623 spectrum analyzer, connect the 300 MHz CAL OUTPUT to the INPUT
5os1.
4. A trace similar to Figure 9-15 indicates a failed crystal-symmetry circuit.
9-30
IF Section